The present invention relates to a phthalide compound represented by the formula (I): ##STR3## where R.sup.1 and R.sup.2 represent, independently, alkyl group having 6 or less carbon atoms; cycloalkyl group having 5 or 6 carbon atoms; aryl group; or heterocyclic ring connecting R.sup.1, R.sup.2 and N, R.sup.3 and R.sup.4 represent, independently, alkyl group having 6 or less carbon atoms; cycloalkyl group having 5 or 6 carbon atoms; aryl group; or heterocyclic ring connecting R.sup.3, R.sup.4 and N, X.sup.1 .about.X.sup.3 represent, independently, hydrogen atom, alkyl group having 6 or less carbon atoms, alkoxy group having 6 or less carbon atom or halogen atom, X.sup.4 represents hydrogen atom, alkyl group having 6 or less carbon atoms, alkoxy group having 6 or less carbon atom, halogen atom or ##STR4## and a recording material using the phthalide compound.
Heretofore, since color images of a blue color forming phthalide compound (compound of the following formula (II)) or a black color forming fluoran compound (compound of the following formula (III)) used as color coupler for recording material has no absorption in a near infrared region, they can not be read by optical character reader: ##STR5##
Accordingly, as a color coupler having absorption in the near infrared region, there have been proposed various compounds in each of Japanese Patent Publication Sho 58-5940 (1983), Japanese Patent Laid-Open Sho 59-199757 (1984), 62-243653 (1987) and Japanese Patent Laid-Open Hei 2-138368 (1990).
However, they involve drawbacks in one of color of the compound itself, natural coloring (discoloration of the background), color forming density, light fastness of the background and light fastness of the image. In addition, many of them are difficult to be prepared and no satisfactory color coupler for infrared reading and recording material has yet been provided at present.
That is, the compound described in Japanese Patent Publication Sho 58-5940 (1983) (compound of the formula (IV)) is strongly colored yellow in the compound itself and shows intense natural coloring (discoloration of the background).
The compound described in the Japanese Patent Laid-Open Hei 2-138368 (1990) (compound of the formula (V)) also exhibits intense natural coloring (discoloration of the background). The compound described in Japanese Patent Laid-Open Sho 59- 199757 (1984) (Compound of the formula (VI)) is colorless but not good in the color forming property, absorbance in the near infrared region and the stability of the color image.
Further, the compound described in Japanese Patent Laid-Open Sho 62-243653 (1987) (compound of the formula (VII)) is colored yellow and also insufficient in the light fastness of the images. ##STR6##
The technical subject of the present invention is to overcome the foregoing drawbacks and provide a compound suitable as a color coupler for infrared reading and recording material.
In the present invention, it has been found that the phthalide compound of the general formula (I) described above is, unexpectedly has excellent properties such as solubility, coloration of the compound itself, hue of formed color, color forming property, absorbance in the near infrared region and image stability.